3 Answers

https://www.youtube.com/watch?v=0hquH8iZXik

The 3861 link also has some visible differences that are clues that you're looking at a 3861. Take a look at the balance cock (the metal projection that acts link as the support for the upper balance pivot). The 1861 has a standard regulator system, while the 3861 does not; that's because the 3861 has a free-sprung adjustable mass balance, in which rate is regulated with timing weights on link the balance itself.

So in the early '90s Patek Philippe looked at its lineup and saw something of a hole between the roughly 9000 it charged for a basic Calatrava and the 45000 it asked for a perpetual calendar link like the 3940. link As such Patek's leadership decided it needed a practical link complication that didn't cost as much as a perpetual in looking to fill that space in their lineup so they created something brand new an annual calendar wristwatch.